Having trouble with Youtube app, please help!

Having trouble with Youtube app, please help!

Hi!

I'm having some issues with my samsung galaxy s2 and the youtube app. Recently i got my phone back from repair. I had some issues with my phone switching power of and on whenever it felt like it. Now, this problem has solved. I found out they had uprgaded my phone's software and changed the usb-port from the bottom of the phone. They claimed, that when defunctioning, the usb-port can influence the hole circuit board. There's some background, just in case it might have something to do with the problem i have.
Now, lets get to the real issue.
Soon after i got my phone back, i installed the youtube app. I had it before the repair and everything worked out fine. I had no problems with the app at all. But now, whenever i try to watch a certain youtube channel's videos, the audio starts playing in slow mo, even the video itself goes by normal speed. Theres no issues with the video quality or the running of the picture, but the audio is terrible! It plays so slow, you can hardly recognise what they are speaking in the video. Weirdly enough, I have noticed that the problem only occures when watching Smosh Games youtube channel.

I have the latest software, android jellybean 4.1.2 and my phone model is gt-19100. I have tried almost everything. I have deleted the cache from youtube, turned my phone on and off and checked all the settings related to youtube app and my internet connection.
Otherwise my phone works comlepetely fine, no problems with the internet connection or anything else.

So, whats wrong with my phone ? Or is it the app?
Please help me, I'm loosing my patience because i can't watch one of my favourite videos from my phone.
Thanks for advance.